Mental Math

Mental Math Shortcuts

Master halving, doubling, decimal shifting, and sum shortcuts to calculate in your head.

Lessons included in this chapter:

• The Foundation: undefined
• Decimal Shifts (10, 100, 1000): undefined
• Multiply by 5: undefined
• Multiply by 4 — Double Twice: undefined
• Multiply by 8 — Triple Double: undefined
• Multiply by 9 — ×10 Minus Trick: undefined
• Multiply by 11 — ×10 + n: undefined
• Multiply by 12, 13, 15: undefined
• Multiply by 25: undefined
• Doubling and Halving: undefined
• Multiplying Numbers Close to 100: undefined
• Difference of Squares: undefined
• Finding the Missing Factor: undefined
• Algebraic Identities as Shortcuts: undefined